Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$154.90	9.677%	$169.8897	$169.89	$169.90	$169.90
Purchase #2	$38.30	8.418%	$41.5241	$41.52	$41.50	$41.50
Purchase #3	$66.57	5.765%	$70.4078	$70.41	$70.40	$70.40
Purchase #4	$74.82	3.362%	$77.3354	$77.34	$77.35	$77.30
Purchase #5	$199.99	10.761%	$221.5109	$221.51	$221.50	$221.50
Purchase #6	$133.72	3.311%	$138.1475	$138.15	$138.15	$138.10
Purchase #7	$63.61	3.504%	$65.8389	$65.84	$65.85	$65.80
7 purchase totals =	$731.91		$784.6543	$784.66	$784.65	$784.50